1. Field of the Invention
The present invention relates to an apparatus employing an inkjet recording method, and more particularly to an apparatus that ejects particulate matter such as pigment matter and toner matter by making use of an electric field.
2. Description of the Related Art
There has recently been a growing interest in non-impact recording methods, because noise while recording is extremely small to such a degree that it can be neglected. Particularly, inkjet recording methods are extremely effective in that they are structurally simple and that they can perform high-speed recording directly onto ordinary medium. One inkjet recording method there is an electrostatic inkjet recording method.
The electrostatic inkjet recording apparatus generally has an electrostatic inkjet recording head and a counter electrode which is disposed behind the recording medium to form an electric field between it and the recording head. The electrostatic inkjet recording head has an ink chamber which temporarily stores ink containing toner particles and a plurality of ejection electrodes formed near the end of the ink chamber and directed toward the counter electrode. The ink near the front end of the ejection electrode forms a concave meniscus due to its surface tension, and consequently, the ink is supplied to the front end of the ejection electrode. If positive voltage relative to the counter electrode is supplied to a certain ejection electrode of the head, then the particulate matter in ink will be moved toward the front end of that ejection electrode by the electric field generated between the ejection electrode and the counter electrode. When the coulomb force due to the electric field between the ejection electrode and the counter electrode considerably exceeds the surface tension of the ink liquid, the particulate matter reaching the front end of the ejection electrode is jetted toward the counter electrode as an agglomeration of particulate matter having a small quantity of liquid, and consequently, the jetted agglomeration adheres to the surface of the recording medium. Thus, by applying pulses of positive voltage to a desired ejection electrode, agglomerations of particulate matter are jetted in sequence from the front end of the ejection electrode, and printing is performed. A recording head such as this is disclosed, for example, in Japan Laid-Open Patent Publication No. 60-228162 and PCT International Publication No. WO93/11866.
Particularly, in the Publication (60-228162), there is disclosed an electrostatic inkjet printer head where a plurality of ejection electrodes are disposed in an ink nozzle, and the front end of each ejection electrode is formed on the projecting portion of a head base which projects from the ink nozzle. The front end of this projecting portion has a pointed configuration, and the ejection electrode is formed in accordance with the direction of the pointed end. An ink meniscus is formed near the front end of the ejection electrode.
However, in the aforementioned conventional electrostatic inkjet recording heads, it is not easy to obtain high resolution, that is, a reduction in the pitch between the ejection electrodes and a fine printing dot. If the pitch between the ejection electrodes is reduced, the ink meniscus will flood the front end of the head base and an undesired ejection of ink will arise from a point differing from the ejection electrode to which a drive pulse signal was applied, and consequently, ejection cannot be performed with high reliability and stability.